smoother edges on acrylic?

[Marc Myer]

I'm making items from acrylic and coating them afterwards with a chrome finish.
When I coat them, the cut edges are too sharp to coat well, and they look bad. I'm trying to figure out how to make them more rounded without time-consuming sanding. Plus, they need to be very smooth to look good.
I've been trying to build gradient 'ramps' next to the vector cuts, but it isn't working yet.
Any ideas?
Here's a sample of a successful one.

[James Stokes]

I am not sure of this but I think if you do that as a rubber stamp it will do what you want.

[Eric Allen]

That is something I've been interested in doing for some time. How do you coat the acrylic?

[rick woodward]

Marc
I had a thought. Might be an idea for you, might not. How about putting the pieces in a dry media tumbler. Like reloaders use (brass bullet cases) Or rock cutters use them to tumble polish stones. If you are doing production. Gotta be some rock hounds around and reloaders. Try it out with their tumblers before getting your own ? Just a thought. rick

[David Epperson]

Two methods come to mind, heat and chemical. Put a test piece in an oven at around 200° (give or take 50° :D ) and see if the edges don't round over a bit. Otherwise treat with an etching solvent, Ethylene (or Methylene) Cloride comes to mind as what I used way back when. Might not be available now though, but was used to do internal polishing of carvings as well as an adhesive solvent on acrylic.
If the parent piece has any internal stresses in it (been stretched or compressed) the heating process will allow it to return to the prestressed shape. So it might be a good idea to heat it before cutting as well just so the finished part remains the same shape. (unless the deformation is part of what you want)

I've still got a nice piece of acrylic from college with 4 curved holes drilled through a 1.5x1.5" cube of clear acrylic. Neat paperweight though. Looks like this [)(]. :D

[Marc Myer]

Thanks, Rick. I'll give that a try--couldn't hurt!

Eric--the coating process is fairly involved, but very cool. It's a three-part catalytic coating system that goes on like paint, basically. There's a primer coat, a two-part metal coating, and a topcoat. It's tough and nice-looking too. It does require an investment in equipment and chemicals, naturally, and precise control of the process. I've had a custom emblem business for several years, and after being let down by suppliers, decided to do it all myself. Profitability? That has yet to be seen...

[Marc Myer]

Wow!
Thanks--I can't wait to try it!

[Rodne Gold]

Flame polish the edges = you need a special flame polisher for this , not a propane type torch although you can use it in a pinch.
Be aware that laser cutting and flame polishing put incredible heat stress into acrylic and any solvents will tend to promote stress cracking on the edges.Dunno if your paint uses solvents?
A deburring tool will also work to take the sharp edges off , albeit you might not get it in all the crevices and its laborious.
Another strategy would be to run the vector cut or or a vector line offset to the inside of the shape you have cut (by a very small amount) at a lower power and out of focus somewhat , this might take the edges off too , I havent tried this tho.
Air assist is VITAL to good edge quality in the vertical cut , it ejects melt and cools just enough to stop remelt but still give a glass finish ,with minimal striations , if set to the correct pressure and direction.

[Eric Allen]

Thanks Marc, where can I dig a bit more into that process? I'd like to see if I can afford to play around with that process a bit:) As to the edges, it seems like I've had luck with focusing a bit close giving me smoother edges. If I didn't have so much demo work to do tonight I'd play with some scrap. Might try a basic vector and see how that works. I've had some odd results at times, like last week when I forgot to refocus for different wood depths, was too far away, and I got the least likely burn I could imagine. It was fat on top (1/8", predictable) and narrowed to a fine kerf as it went deeper. Since I was too far away to begin with, that's totally counterintuitive to how I thought it would work, should have gotten larger as it went farther in. That kind of odd stuff is what makes me experiment more:) Not sure how much smoothing you need, but it seems like my edges on business cards and such are pretty smooth on top, the bottom of the cut is always sharp.

[rick woodward]

Marc
If you would, after trying out these ideas, let us know the results ? That way it would possibly help others . Also, there are different dry media that can be used in a tumbler. One of them should give you what you need without damage. Plus you can toss them in, turn it on and walk away. set a timer to let you know when they are done and load it up again. only ongoing expense is electricity. And your freed up to do other things while it tumbles. Low cost,low maintenance and should be quality results. Best wishes, mister.:)

[Bob Cole]

I was curious of a tumbler would work on the different materials. I have a Dillon tumbler that I use when reloading brass, so wanted to try on other materials to see the effect.

I've used crushed walnuts for brass, but what would you recommend to use for acrylic in your tumbler?

[Chris McDonald]

To make my top edge of my acrylic rounded i bring the laser out of focus about .150" or more.

Chris

[Bill Cunningham]

I was curious of a tumbler would work on the different materials. I have a Dillon tumbler that I use when reloading brass, so wanted to try on other materials to see the effect.

I've used crushed walnuts for brass, but what would you recommend to use for acrylic in your tumbler?

Walnut shells should work on Acrylic too! If not, use aquarium gravel..I was too cheap to buy the Dillon tumbler, a HD 5 gal bucket with a lazyboy vibrator screwed to the bottom works great for cleaning .40 cal brass 50/50 corncobb/walnut..

[Brian Robison]

To make my top edge of my acrylic rounded i bring the laser out of focus about .150" or more.

Chris

Hi Chris, out of focus meaning farther away?

[Mark Winlund]

Flame polishing can be done fairly easily with an oxygen - hydrogen torch. Contact your local welding supplier for the equipment. It is fairly inexpensive compared to a laser. The edge of the acrylic must be reasonably smooth.... routed, or saw cut with a carbide blade. It works well because there is no carbon in the flame. Nearly invisible flame.

Mark

[Chris McDonald]

Hi Chris, out of focus meaning farther away?


Yes the beam will be a little weaker/wider. I find it rounds the top edge off a little.

Chris

[Marc Myer]

Update:
After some experimentation, I have found some success by following advice and doing two passes. One is a normal vector cut, the other is a cut at twice the speed, and brought out of focus by about 1 inch. The more rounded edge seems to work well; the coatings are adhering much better now.

I didn't get a chance to try the walnut blasting: I visited a blasting supplier and chose not to buy the 50-lb bag of walnut shells just to experiment.

I didn't have much luck with a second (inset) vector line, but If I combined it with the out-of-focus trick, it may work. The refinement continues... Thanks, all.

[Bill Cunningham]

If you want to try a smaller quantity of walnut shells and corn cob, for blasting, or cleaning your reloads try your local pets smart (or any pet store) the rich cats use it for litter..:D